a) Field of the Invention
The present invention relates to a camshaft phase changing apparatus for varying a timing of a valve actuation for an engine driven camshaft.
b) Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 7-139316 published on May 30, 1995 exemplifies a previously proposed camshaft phase changing apparatus in an internal combustion engine.
The previously proposed camshaft phase changing apparatus disclosed in the above-identified Japanese Patent Application First Publication includes: a cylindrical timing pulley to which a torque is transmitted from a timing belt via a crankshaft of the engine; a camshaft having a cam on an outer peripheral surface thereof and a sleeve fixed on one end of the camshaft and inserted into a cylindrical main body of the timing pulley; and a cylindrical gear which is enabled to move in a forward-and-rearward direction thereof and is meshed via outer and inner beveled teeth thereof with the cylindrical main body of the timing pulley and the sleeve.
The previously proposed camshaft phase changing apparatus further includes: advance-angle side and retardation-angle side hydraulic chambers formed within an internal of the cylindrical main body of the timing pulley, into which pressurized working oil is supplied via a hydraulic circuit, and from which the pressurized working oil is exhausted via the hydraulic circuit. Hence, the cylindrical gear is moved in the forward-and-rearward direction thereof according to a difference in the hydraulic pressures in the advance-angle side hydraulic chamber and the retardation-angle side hydraulic chamber so that a relative rotational phase between the timing pulley and the camshaft is converted. Thus, a valve-opening-and-closing timing thereof, for example, a suction valve is controlled toward an advance angle side or toward a retardation angle side.
In addition, a hydraulic control valve is interposed in hydraulic passages communicating the respective advance-angle side and retardation-angle side hydraulic chambers with a working oil pump.
A spool valve body having a large-diameter portion and small-diameter portion is slidably held within a cylindrical valve seat. In addition, a plurality of openings communicating with the hydraulic passage are formed at predetermined positions on a peripheral wall of the valve seat along an axial direction of the spool valve body. In order to render a leaked working oil to fall within an allowable range, a seal length of the adjacent openings having a high hydraulic pressure difference is set to be elongated and the seal length between the adjacent openings having a low hydraulic pressure difference is set to be short. Consequently, an axial length of the whole valve seat can be shortened.